This invention relates to a method of aralkylating benzene or alkylbenzenes (hereinafter referred to generically as "alkylbenzenes"). More particularly, this invention is concerned with a method of adding aromatic olefins (hereinafter referred to generically as "styrenes") having a double bond in the position conjugated with the benzene ring to alkylbenzenes in high yield in the addition of olefins or mixtures thereof to alkylbenzenes.
The reaction of adding various olefins to alkylbenzenes is known as Friedel-Crafts reaction and as an important reaction from the standpoint of chemical industry. This addition reaction is classified into an alkylation reaction of alkylbenzenes with aliphatic compounds having an olefinic double bond (hereinafter referred to as "aliphatic olefins"), and an aralkylation of styrenes with alkylbenzenes. The term "olefins" is a general term for both aliphatic olefins (including the so-called diolefins) and aromatic olefins (including styrenes). These terms will be used hereinafter.
Alkylated compounds are used as a starting material in the chemical industry, and per se are used as an insulating or lubricating oil. On the other hand, aralkylated compounds, which are superior in heat resistance, compatibility and electrical characteristics, are known as an industrially preferred aromatic synthetic oil suitable for a heat transfer medium, a plasticizer, a reaction solvent and an insulating oil. Because of the difficulty in the manufacturing process, however, there is only a limited number of chemical enterprises which manufacture such aralkylated compounds independently.
Aralkylated compounds, in their basic chemical structure, have the diphenylmethane skeleton in which two benzene rings are bonded to the same carbon atom. Consequently, unlike alkylnaphthalenes and alkylbiphenyls which have been known as high-boiling aromatic synthetic oils, aralkylated compounds are characteristic in that they are a non-condensed polycyclic aromatic synthetic oil.
Known as the method of obtaining aralkylated compounds is one in which an aralkylation reaction is carried out using halogenated alkylbenzenes with the .alpha.-position of alkyl group substituted by a halogen atom and in the presence of a halogenated metallic catalyst such as aluminum chloride, and one in which an aralkylation reaction is carried out using styrenes and in the presence of an acid catalyst. When consideration is given as to whether it is easy or not to treat the by-produced hydrogen halide and to obtain an aralkylating agent .alpha.-halogenated alkylbenzenes, the latter method of aralkylation using styrenes in the presence of an acid catalyst is preferred.
As the aralkylation method using styrenes heretofore disclosed there are known the method using a sulfuric acid catalyst shown in British Pat. No. 977,322 and the method using a solid acid catalyst shown in British Pat. No. 896,864.
It goes without saying that, among these catalysts, it is solid acid catalysts that can be used preferably in practical application because of their easiness of separation or removal of catalysts after reaction.
Among solid acid catalysts, moreover, we have found that acidic ion-exchange resins exhibit an activity in the aralkylation reaction.
However, conventional acidic ion-exchange resins, in which a sulfonated styrene-divinylbenzene copolymer is a backbone polymer, are low in aralkylation activity and are further disadvantageous in that, if the reaction temperature is raised with the object of attaining a sufficient activity, the catalyst particles will be destroyed and the acid component will flow out, resulting in the catalyst life being shortened and in the necessity of neutralizing the acid component which has flowed out into the reaction solution.
In the aralkylation reaction using such conventional acidic ion-exchange resins, moreover, there are easily produced dimers or polymers of styrenes because styrenes, particularly styrene, have a much higher polymerization activity than aliphatic olefins such as ethylene and propylene. Also from this point conventional acidic ion-exchange resins have not been preferable.
It is an object of this invention to eliminate the above-mentioned drawbacks associated with the prior art aralkylation.
It is another object of this invention to provide a method of aralkylating alkylbenzenes with less formation of by-products and in high selectivity.
It is a further object of this invention to provide a new aralkylation catalyst of high activity superior in stability and durability.
Other objects of this invention will become clear from the following description.
The aforesaid objects of this invention can be attained by contacting an aromatic olefin having an olefinic double bond conjugated with the benzene ring, with benzene or an alkylbenzene containing alkyl group(s) with a total number of carbon atom of the alkyl group(s) ranging from 1 to 18, at a temperature of 50.degree. to 230.degree. C. and in the presence of a perfluoro polymer having as a repeating unit at least one unit selected from units represented by the general formulae ##STR1## where, n is an integer of 0, 1, or 2,
R is a fluorine atom or a perfluoroalkyl group of C.sub.1 to C.sub.10, PA1 X is --O(CF.sub.2).sub.m -- wherein m is an integer of 1 to 10, --OCF.sub.2 CFY--, or --OCFYCF.sub.2 --, and PA1 Y is a fluorine atom or trifluoromethyl group. PA1 R is a fluorine atom or a perfluoroalkyl of C.sub.1 to C.sub.10, PA1 X is --O(CF.sub.2).sub.m -- wherein m is an integer of 1 to 10, --OCF.sub.2 CFY--, or --OCFYCF.sub.2 --, and PA1 Y is a fluorine atom or trifluoromethyl group. PA1 x, y and z are integers having next relations PA1 x/y=2 to 20 PA1 z=500 to 10000
The aralkylation catalyst used in the method of this invention is a solid, resinous high polymer.
The said catalyst is a perfluoro resinous high polymer (hereinafter referred to as the "resin catalyst") having an acid strength of 0.01 to 5 milliequivalent/g.
Such resin catalyst is characterized by being a polymer having a repeating unit represented by the following general formula (I) or (II): ##STR2## where, n is an integer of 0, 1, or 2,